/**
 * Style markers — how layout structure survives a round-trip through draw.io.
 *
 * The layout engine's tree carries information plain draw.io XML does not: which
 * direction a container stacks its children, the gap between them, and whether the
 * user has pinned a node's position. We encode that as extra `key=value` tokens in
 * the cell's style string.
 *
 * Two behaviours this relies on, both verified in a real browser (Playwright drag
 * against the embedded editor, reading the editor's own autosave payload):
 *
 *   1. draw.io PRESERVES style keys it does not understand. After a user drags a
 *      shape and the editor saves, `dai_kind=group;dai_dir=col;dai_gap=22;` came
 *      back byte-identical.
 *   2. On a DUPLICATE key, the LAST value wins. A style ending in
 *      `container=0;pointerEvents=0;container=1;` behaved as a container: a shape
 *      dragged into it was reparented. So we can append a normalising token without
 *      first parsing out the old one.
 *
 * (2) matters because the AWS catalog is inconsistent: group_region, group_vpc,
 * group_subnet, group_availability_zone, group_aws_cloud and group_on_premise ship
 * WITHOUT container=1, while group_account, group_aws_cloud_alt, group_vpc2,
 * group_security_group and group_corporate_data_center ship WITH it. Appending
 * unconditionally normalises all of them.
 */

/** Marker keys. Namespaced with `dai_` so they cannot collide with mxGraph keys. */
export const MARKER = {
    /** Node kind, so the parser does not have to re-guess it from the shape. */
    kind: "dai_kind",
    /** Child stacking direction of a container: "row" | "col" | "grid". */
    dir: "dai_dir",
    /** Gap between children, in px. */
    gap: "dai_gap",
    /** Column count, for grid containers. */
    cols: "dai_cols",
    /** Set by the user to freeze a node's position across re-layouts. */
    pin: "dai_pin",
    /**
     * A catalog icon's name. Needed because an Azure or GCP icon's style is an embedded
     * base64 image with no name anywhere in it, so the style alone cannot identify it.
     */
    name: "dai_name",
    /**
     * Which (lane, column) cell of a swimlane pool a node occupies, as "lane,col".
     *
     * Position alone cannot recover this once the user drags a node: the cell it lands in
     * is a guess, whereas the marker records which lane the model assigned it to. It is
     * also the only way an empty cell stays empty — geometry can only tell us where things
     * ARE, never that a role deliberately does nothing at a given step.
     */
    cell: "dai_cell",
    /** A pool's lane names, tab-separated (a tab cannot appear in a draw.io style value). */
    lanes: "dai_lanes",
    /** A pool's milestone labels, tab-separated. */
    phases: "dai_phases",
    /** A pool's orientation: "h" or "v". */
    orient: "dai_orient",
    /** Vertical distance between consecutive messages in a sequence diagram. */
    step: "dai_step",
    /** How a radial container fans its branches out: "radial" or "down". */
    spread: "dai_spread",
    /** The node's information role (banner, heading, callout…), for the round trip. */
    role: "dai_role",
    /** The node's semantic zone, whose hue ramp colours it. */
    group: "dai_group",
    /**
     * The declared shape token, verbatim. Appearance-based reverse mapping is ambiguous
     * (aliases, rotated variants, styles with no unique shape= token), so the round trip
     * carries the declaration itself.
     */
    shape: "dai_shape",
    /**
     * Marks a node's size as engine-computed rather than user-fixed. Without it, the
     * w/h read back from the canvas would freeze the first layout's measurement: change
     * the label and the box would keep the old size instead of re-measuring.
     */
    auto: "dai_auto",
    /** Share of the parent's leftover flow-axis space — flex-grow. */
    grow: "dai_grow",
    /** Cross-axis position within the parent: "start" | "center" | "end". */
    align: "dai_align",
    /** How a container spreads children along its own axis — justify-content. */
    justify: "dai_justify",
    /** A container's cross-axis default for children that declare no align of their own. */
    alignItems: "dai_aitems",
    /** Opted out of the content-width floor when weights divide a row — CSS's min-width:0. */
    minw0: "dai_minw0",
    /**
     * Declared width cap, px.
     *
     * Has to be a marker rather than inferred from the drawn width: the two are only equal
     * when the cap actually bit. A box capped at 400 that happens to be 260 wide would come
     * back with a 260 cap, and the next re-layout could never let it grow again.
     */
    maxw: "dai_maxw",
    /** A container's interior padding, px. */
    pad: "dai_pad",
    /**
     * The page's declared width:height, on the default layer's cell.
     *
     * Page-level rather than per-node, so it goes on layer "1" — the one cell every
     * diagram has and draw.io never discards. It cannot be inferred from pageWidth and
     * pageHeight: those are what the last layout produced, so reading them back would
     * turn whatever shape a diagram happened to come out as into a standing request to
     * keep it.
     */
    aspect: "dai_aspect",
    /**
     * Marks a cell as chrome the engine draws and owns: a pool's lane bands, its label
     * columns, its milestone strip. The parser must not read these back as nodes — they are
     * re-derived from the pool's own parameters on every layout — and the edge router must
     * not treat them as obstacles, since a sequence flow crossing lanes is the norm.
     */
    lane: "dai_lane",
} as const

export type NodeKind =
    | "group"
    | "grid"
    | "pool"
    | "sequence"
    | "radial"
    | "icon"
    | "box"
    | "title"
export type Direction = "row" | "col" | "grid"

/**
 * Tokens that make a shape behave as a container in draw.io: it accepts a shape
 * dragged into it and reparents that shape (setting `parent` and switching the
 * child's geometry to parent-relative).
 *
 * `pointerEvents=0` keeps clicks falling through to the children — without it the
 * frame swallows them and the user cannot select what is inside. `collapsible=0`
 * hides the fold arrow. `recursiveResize=0` stops children from being scaled when
 * the frame is resized, which would fight the layout engine.
 */
const CONTAINER_TOKENS =
    "container=1;pointerEvents=0;collapsible=0;recursiveResize=0;"

/**
 * A container that groups children for layout but should not be visible.
 *
 * The reference project solves this with a "phantom": a wrapper that participates in
 * layout and then emits NO cell, reparenting its children onto the nearest visible
 * ancestor. That makes the round-trip lossy by construction — the wrapper's direction
 * and grouping are simply absent from the XML, so re-deriving the tree cannot recover
 * them. Measured on the reference project's own build_vpc.mjs: a phantom erased a
 * container's "col" direction, leaving children in a 2-D arrangement that can only be
 * read back as a grid.
 *
 * So we emit a real cell and make it invisible instead. One extra cell per wrapper,
 * in exchange for structure that survives being read back.
 */
const INVISIBLE_TOKENS = "fillColor=none;strokeColor=none;"

/** Read a marker's raw value out of a style string. Last occurrence wins, as draw.io does. */
export function readMarker(style: string, key: string): string | null {
    // Scan all matches and keep the last, mirroring draw.io's duplicate-key resolution.
    const re = new RegExp(`(?:^|;)${key}=([^;]*)`, "g")
    let last: string | null = null
    let m = re.exec(style)
    while (m !== null) {
        last = m[1]
        m = re.exec(style)
    }
    return last
}

const KINDS: readonly NodeKind[] = [
    "group",
    "grid",
    "pool",
    "sequence",
    "radial",
    "icon",
    "box",
    "title",
]

export function readKind(style: string): NodeKind | null {
    const v = readMarker(style, MARKER.kind)
    return KINDS.includes(v as NodeKind) ? (v as NodeKind) : null
}

/**
 * The (lane, column) cell a node occupies in a swimlane pool, or null.
 *
 * Both must be non-negative integers: a malformed value is safer read as "no cell
 * declared" (which puts the node in lane 0 column 0) than as a negative index, which would
 * place it outside the pool's frame.
 */
export function readCell(style: string): { lane: number; col: number } | null {
    const v = readMarker(style, MARKER.cell)
    if (!v) return null
    const m = v.match(/^(\d+),(\d+)$/)
    return m ? { lane: Number(m[1]), col: Number(m[2]) } : null
}

/**
 * A tab-separated marker list, as written by `joinList`.
 *
 * A tab cannot appear in a draw.io style value — the editor writes styles as a single
 * semicolon-separated line — so it is safe as a separator inside one value, where a comma
 * would collide with the label text it has to carry.
 */
export function readList(style: string, key: string): string[] | null {
    const v = readMarker(style, key)
    if (v === null) return null
    if (v === "") return []
    return v.split("\t").map(decodeURIComponent)
}

/** Encode a list of labels into one marker value. */
export function joinList(items: string[]): string {
    // Percent-encoding keeps a label containing ";" or "=" from breaking the style string.
    return items.map((s) => encodeURIComponent(s)).join("\t")
}

/** Is this cell pool chrome the engine draws and owns, rather than a node? */
export function isLaneChrome(style: string): boolean {
    return readMarker(style, MARKER.lane) !== null
}

export function readDir(style: string): Direction | null {
    const v = readMarker(style, MARKER.dir)
    if (v === "row" || v === "col" || v === "grid") return v
    return null
}

/** Read a positive integer marker (gap, cols). Returns null when absent or malformed. */
export function readIntMarker(style: string, key: string): number | null {
    const v = readMarker(style, key)
    if (v === null) return null
    const n = Number(v)
    return Number.isFinite(n) && n >= 0 ? Math.round(n) : null
}

/**
 * Has the user pinned this node? Any value other than "0"/""/"false" counts as
 * pinned, so a user typing `dai_pin=1` (or just `dai_pin=yes`) in draw.io's
 * "Edit Style" dialog gets what they expect.
 */
export function isPinned(style: string): boolean {
    const v = readMarker(style, MARKER.pin)
    if (v === null) return false
    const s = v.trim().toLowerCase()
    return s !== "" && s !== "0" && s !== "false"
}

/**
 * Append `key=value;`, replacing any existing occurrence of the key first.
 *
 * Styles are re-stamped on every render, and a style recovered from the canvas already
 * carries last render's markers — blindly appending grew the string by one duplicate per
 * round-trip, unboundedly. Duplicates resolve last-wins in draw.io so nothing ever LOOKED
 * wrong, which is why it went unnoticed until a byte-identity test caught it.
 *
 * Only `dai_*` keys are cleaned. mxGraph keys are appended verbatim because last-wins is
 * load-bearing there: the container tokens rely on appending `container=1` after a catalog
 * style that may say `container=0`.
 */
/**
 * Set each `key=value;` token of `tokens` on a style, replacing any value already there.
 *
 * Matching is per token, not on the whole run: a catalog style may already declare
 * `container=1` while saying nothing about `pointerEvents`, and re-adding the whole run
 * because one token was missing is what let these accumulate.
 *
 * Exported because the same defect appeared a second time, on EDGES: an edge's style starts
 * from whatever the canvas held, which already carried the previous pass's `exitX`/`entryX`
 * port keys, and the router appended a fresh set on top of them every render — 76 characters
 * per round-trip, without bound. Any code that re-stamps a computed mxGraph key onto a style
 * recovered from the canvas needs this rather than `+=`.
 */
export function appendOnce(style: string, tokens: string): string {
    let s = style
    for (const tok of tokens.split(";")) {
        if (!tok) continue
        const key = tok.slice(0, tok.indexOf("="))
        // The key must not be present with ANY value: `container=0` from a catalog stencil
        // has to be overwritten, which is what appending the correct value does.
        const has = new RegExp(`(?:^|;)${key}=[^;]*;`).test(s)
        if (has) {
            s = s.replace(new RegExp(`(?:^|(?<=;))${key}=[^;]*;`, "g"), "")
        }
        s = s.endsWith(";") || s === "" ? s : `${s};`
        s += `${tok};`
    }
    return s
}

function append(style: string, key: string, value: string | number): string {
    const cleaned = key.startsWith("dai_")
        ? style.replace(new RegExp(`(?:^|(?<=;))${key}=[^;]*;`, "g"), "")
        : style
    const base =
        cleaned.endsWith(";") || cleaned === "" ? cleaned : `${cleaned};`
    return `${base}${key}=${value};`
}

/**
 * Stamp a container's style: make it a real draw.io container and record its
 * layout parameters.
 *
 * Appends rather than rewrites. Duplicate keys are legal and the last one wins, so
 * a catalog style that already says `container=1` is unharmed, and one that says
 * nothing (or `container=0`) is corrected.
 */
export function stampContainer(
    style: string,
    opts: {
        kind: "group" | "grid"
        dir: Direction
        gap: number
        cols?: number
        /** Layout-only wrapper: emit a real cell, but draw nothing. */
        invisible?: boolean
    },
): string {
    let s = style.endsWith(";") || style === "" ? style : `${style};`
    // Appended only when not already there. These are plain mxGraph keys, so `append`'s
    // de-duplication (which is limited to `dai_*`) does not cover them — and a container
    // goes through here on EVERY re-layout, so a blind `+=` grew the style string by
    // another `container=1;pointerEvents=0;collapsible=0;recursiveResize=0;` per round
    // trip, without bound. Harmless to draw.io, which takes the last value, but the XML
    // never reached a fixed point and every edit shipped a longer style.
    s = appendOnce(s, CONTAINER_TOKENS)
    if (opts.invisible) s = appendOnce(s, INVISIBLE_TOKENS)
    s = append(s, MARKER.kind, opts.kind)
    s = append(s, MARKER.dir, opts.dir)
    s = append(s, MARKER.gap, Math.round(opts.gap))
    if (opts.kind === "grid" && opts.cols != null)
        s = append(s, MARKER.cols, Math.max(1, Math.round(opts.cols)))
    return s
}

/**
 * Stamp a swimlane pool: its lane names, milestone labels and orientation.
 *
 * Unlike a group, a pool is NOT stamped as a draw.io container. Its lane bands are separate
 * cells sitting inside it, and they are what a shape should reparent into when the user
 * drags it — that is how "the user moved this step to a different role" gets recorded. If
 * the pool itself claimed the drop, every node would come back in lane 0.
 */
export function stampPool(
    style: string,
    opts: {
        lanes: string[]
        phases: string[]
        orientation: "horizontal" | "vertical"
        gap: number
    },
): string {
    let s = append(style, MARKER.kind, "pool")
    s = append(s, MARKER.lanes, joinList(opts.lanes))
    s = append(s, MARKER.phases, joinList(opts.phases))
    s = append(s, MARKER.orient, opts.orientation === "vertical" ? "v" : "h")
    return append(s, MARKER.gap, Math.round(opts.gap))
}

/** Stamp a sequence container: participant spacing and message spacing. */
export function stampSequence(
    style: string,
    opts: { gap: number; step: number },
): string {
    const s = append(style, MARKER.kind, "sequence")
    return append(
        append(s, MARKER.gap, Math.round(opts.gap)),
        MARKER.step,
        Math.round(opts.step),
    )
}

/** Stamp a radial container: how it fans branches out, and the ring spacing. */
export function stampRadial(
    style: string,
    opts: { spread: "radial" | "down"; gap: number },
): string {
    const s = append(style, MARKER.kind, "radial")
    return append(
        append(s, MARKER.spread, opts.spread),
        MARKER.gap,
        Math.round(opts.gap),
    )
}

/**
 * Stamp one of a pool's lane bands.
 *
 * A band IS a draw.io container, so dragging a step onto another role's band reparents it
 * there and the marker on the band tells the parser which lane that is. The lane index is
 * the band's identity, not its position, so the assignment survives the pool being
 * re-measured to a different size.
 */
export function stampLane(style: string, lane: number): string {
    let s = style.endsWith(";") || style === "" ? style : `${style};`
    s += CONTAINER_TOKENS
    return append(s, MARKER.lane, Math.max(0, Math.round(lane)))
}

/**
 * Stamp a pool's own decoration — a lane-name column or a milestone strip.
 *
 * `dai_lane=-1` marks it as chrome the renderer rebuilds, so the parser drops it rather
 * than reading it back as a node. Unlike a lane band it is deliberately NOT a draw.io
 * container: a step dropped on a label column belongs to no role, and letting it reparent
 * there would lose the step's lane.
 */
export function stampPoolDecoration(style: string): string {
    return append(style, MARKER.lane, -1)
}

/** Record which pool cell a node occupies. */
export function stampCell(
    style: string,
    cell: { lane: number; col: number },
): string {
    return append(
        style,
        MARKER.cell,
        `${Math.max(0, Math.round(cell.lane))},${Math.max(0, Math.round(cell.col))}`,
    )
}

/**
 * Is this an invisible layout wrapper? Both colours set to `none` and no group
 * stencil — a visible frame always has a stroke or a stencil.
 */
export function isInvisible(style: string): boolean {
    if (/grIcon=/.test(style)) return false
    const fill = readMarker(style, "fillColor")
    const stroke = readMarker(style, "strokeColor")
    return fill === "none" && stroke === "none"
}

/**
 * Stamp a leaf with its kind, so the parser need not infer it.
 *
 * For an icon, also record the catalog name: an Azure or GCP icon's style is an embedded
 * base64 image with no name in it, so the style alone cannot identify which icon it is.
 */
export function stampLeaf(
    style: string,
    kind: "icon" | "box" | "title",
    opts: { name?: string } = {},
): string {
    const s = append(style, MARKER.kind, kind)
    return opts.name ? append(s, MARKER.name, opts.name) : s
}

/** Stamp the node's information role, replacing any previous one. */
export function stampRole(style: string, role: string): string {
    return append(style, MARKER.role, role)
}

/** Stamp the node's semantic zone, replacing any previous one. */
export function stampGroup(style: string, group: string): string {
    return append(style, MARKER.group, encodeURIComponent(group))
}

/** Stamp the declared shape token, so the round trip carries the declaration itself. */
export function stampShape(style: string, shape: string): string {
    return append(style, MARKER.shape, encodeURIComponent(shape))
}

/** Mark a node's size as engine-computed, so a re-layout re-measures it. */
export function stampAuto(style: string): string {
    return append(style, MARKER.auto, 1)
}

/** Was this node's size computed by the engine (vs fixed by the user or the model)? */
export function isAutoSized(style: string): boolean {
    return readMarker(style, MARKER.auto) === "1"
}

type FlexAlign = "start" | "center" | "end" | "stretch"
type FlexJustify = "start" | "center" | "end" | "between" | "around" | "evenly"

/** Stamp the flex fields a node carries, so a round-trip preserves them. */
export function stampFlex(
    style: string,
    opts: {
        grow?: number
        align?: FlexAlign
        justify?: FlexJustify
        alignItems?: FlexAlign
        maxW?: number
        minW0?: boolean
        pad?: number
    },
): string {
    let s = style
    if (opts.grow != null && opts.grow > 0)
        s = append(s, MARKER.grow, opts.grow)
    if (opts.align && opts.align !== "center")
        s = append(s, MARKER.align, opts.align)
    if (opts.justify && opts.justify !== "start")
        s = append(s, MARKER.justify, opts.justify)
    if (opts.alignItems) s = append(s, MARKER.alignItems, opts.alignItems)
    if (opts.maxW != null && opts.maxW > 0)
        s = append(s, MARKER.maxw, Math.round(opts.maxW))
    if (opts.minW0) s = append(s, MARKER.minw0, 1)
    if (opts.pad != null) s = append(s, MARKER.pad, Math.round(opts.pad))
    return s
}

/** Read the align marker back. Anything unrecognised means the default (center). */
export function readAlign(style: string): Exclude<FlexAlign, "center"> | null {
    const v = readMarker(style, MARKER.align)
    return v === "start" || v === "end" || v === "stretch" ? v : null
}

/** Read a container's cross-axis default. Null means it declared none. */
export function readAlignItems(style: string): FlexAlign | null {
    const v = readMarker(style, MARKER.alignItems)
    return v === "start" || v === "end" || v === "stretch" || v === "center"
        ? v
        : null
}

/** Read the justify marker back. Anything unrecognised means the default (start). */
export function readJustify(
    style: string,
): Exclude<FlexJustify, "start"> | null {
    const v = readMarker(style, MARKER.justify)
    return v === "center" ||
        v === "end" ||
        v === "between" ||
        v === "around" ||
        v === "evenly"
        ? v
        : null
}

/** Read the declared width cap back, or null when there was none. */
export function readMaxW(style: string): number | null {
    const v = Number(readMarker(style, MARKER.maxw))
    return Number.isFinite(v) && v > 0 ? v : null
}

/** Did this node opt out of the content-width floor? */
export function readMinW0(style: string): boolean {
    return readMarker(style, MARKER.minw0) === "1"
}

/** The page's declared aspect ratio, stamped on the default layer. */
export function stampAspect(layerXml: string, aspect: number): string {
    return layerXml.replace(
        /<mxCell id="1" parent="0"\/>/,
        `<mxCell id="1" parent="0" style="${MARKER.aspect}=${aspect};"/>`,
    )
}

/**
 * Read the page's declared aspect back out of a model body.
 *
 * Scans for the marker anywhere in the page rather than parsing the layer cell: the
 * marker name is namespaced, so a match cannot be anything else, and this keeps working
 * if draw.io ever reorders or reformats that cell.
 */
export function readAspect(page: string): number | undefined {
    const m = new RegExp(`${MARKER.aspect}=([\\d.]+)`).exec(page)
    if (!m) return undefined
    const v = Number(m[1])
    return Number.isFinite(v) && v > 0
        ? Math.min(4, Math.max(0.25, v))
        : undefined
}

/** Strip every `dai_*` marker — for exporting a clean file, or comparing styles. */
export function stripMarkers(style: string): string {
    return style
        .split(";")
        .filter((tok) => tok !== "" && !tok.startsWith("dai_"))
        .join(";")
        .concat(";")
        .replace(/^;$/, "")
}

/** Does this style carry any engine marker? Used to tell engine output from imported files. */
export function hasMarkers(style: string): boolean {
    return /(?:^|;)dai_[a-z]+=/.test(style)
}