message-ids.ts

import type { SessionState, WithParts } from "./state"

const MESSAGE_REF_REGEX = /^m(\d{4})$/
const BLOCK_REF_REGEX = /^b([1-9]\d*)$/
const MESSAGE_ID_TAG_NAME = "dcp-message-id"

const MESSAGE_REF_WIDTH = 4
const MESSAGE_REF_MIN_INDEX = 0
export const MESSAGE_REF_MAX_INDEX = 9999

export type ParsedBoundaryId =
    | {
          kind: "message"
          ref: string
          index: number
      }
    | {
          kind: "compressed-block"
          ref: string
          blockId: number
      }

export function formatMessageRef(index: number): string {
    if (
        !Number.isInteger(index) ||
        index < MESSAGE_REF_MIN_INDEX ||
        index > MESSAGE_REF_MAX_INDEX
    ) {
        throw new Error(
            `Message ID index out of bounds: ${index}. Supported range is 0-${MESSAGE_REF_MAX_INDEX}.`,
        )
    }
    return `m${index.toString().padStart(MESSAGE_REF_WIDTH, "0")}`
}

export function formatBlockRef(blockId: number): string {
    if (!Number.isInteger(blockId) || blockId < 1) {
        throw new Error(`Invalid block ID: ${blockId}`)
    }
    return `b${blockId}`
}

export function parseMessageRef(ref: string): number | null {
    const normalized = ref.trim().toLowerCase()
    const match = normalized.match(MESSAGE_REF_REGEX)
    if (!match) {
        return null
    }
    const index = Number.parseInt(match[1], 10)
    return Number.isInteger(index) ? index : null
}

export function parseBlockRef(ref: string): number | null {
    const normalized = ref.trim().toLowerCase()
    const match = normalized.match(BLOCK_REF_REGEX)
    if (!match) {
        return null
    }
    const id = Number.parseInt(match[1], 10)
    return Number.isInteger(id) ? id : null
}

export function parseBoundaryId(id: string): ParsedBoundaryId | null {
    const normalized = id.trim().toLowerCase()
    const messageIndex = parseMessageRef(normalized)
    if (messageIndex !== null) {
        return {
            kind: "message",
            ref: formatMessageRef(messageIndex),
            index: messageIndex,
        }
    }

    const blockId = parseBlockRef(normalized)
    if (blockId !== null) {
        return {
            kind: "compressed-block",
            ref: formatBlockRef(blockId),
            blockId,
        }
    }

    return null
}

export function formatMessageIdTag(ref: string): string {
    return `\n<${MESSAGE_ID_TAG_NAME}>${ref}</${MESSAGE_ID_TAG_NAME}>`
}

export function assignMessageRefs(state: SessionState, messages: WithParts[]): number {
    let assigned = 0

    for (const message of messages) {
        const rawMessageId = message.info.id
        if (typeof rawMessageId !== "string" || rawMessageId.length === 0) {
            continue
        }

        const existingRef = state.messageIds.byRawId.get(rawMessageId)
        if (existingRef) {
            if (state.messageIds.byRef.get(existingRef) !== rawMessageId) {
                state.messageIds.byRef.set(existingRef, rawMessageId)
            }
            continue
        }

        const ref = allocateNextMessageRef(state)
        state.messageIds.byRawId.set(rawMessageId, ref)
        state.messageIds.byRef.set(ref, rawMessageId)
        assigned++
    }

    return assigned
}

function allocateNextMessageRef(state: SessionState): string {
    let candidate = Number.isInteger(state.messageIds.nextRef)
        ? Math.max(MESSAGE_REF_MIN_INDEX, state.messageIds.nextRef)
        : MESSAGE_REF_MIN_INDEX

    while (candidate <= MESSAGE_REF_MAX_INDEX) {
        const ref = formatMessageRef(candidate)
        if (!state.messageIds.byRef.has(ref)) {
            state.messageIds.nextRef = candidate + 1
            return ref
        }
        candidate++
    }

    throw new Error(
        `Message ID alias capacity exceeded. Cannot allocate more than ${formatMessageRef(MESSAGE_REF_MAX_INDEX)} aliases in this session.`,
    )
}