import { CommitsResponse } from "./requests.js";
import { SECONDS_PER_DAY } from "./util.js";

type Commit = {
    indexByHash: number;
    indexByGraph: number;
    hash: string;
    parents: Commit[];
    children: Commit[];
    author: string;
    committerDate: number;
    summary: string;
};

export class Commits {
    #graphId: number | null = null;
    #commitsByGraph: Commit[] = [];
    #committerDatesNormal: Date[] = [];
    #committerDatesDayEquidistant: Date[] = [];

    requiresUpdate(graphId: number): boolean {
        return this.#graphId === null || this.#graphId < graphId;
    }

    update(response: CommitsResponse) {
        console.assert(response.hashByHash.length == response.authorByHash.length);
        console.assert(response.hashByHash.length == response.committerDateByHash.length);
        console.assert(response.hashByHash.length == response.summaryByHash.length);

        let commits = this.#loadCommits(response);
        commits = this.#sortCommitsTopologically(commits);
        this.#sortCommitsByCommitterDate(commits);

        // Fill in indexes - "later" is now
        for (const [idx, commit] of commits.entries()) {
            commit.indexByGraph = idx;
        }

        const committerDatesNormal = commits.map(c => c.committerDate);
        const committerDatesDayEquidistant = this.#makeDayEquidistant(committerDatesNormal);

        // To prevent exceptions and other weirdness from messing up our state,
        // we update everything in one go.
        this.#graphId = response.graphId;
        this.#commitsByGraph = commits;
        this.#committerDatesNormal = this.#epochTimesToDates(committerDatesNormal);
        this.#committerDatesDayEquidistant = this.#epochTimesToDates(committerDatesDayEquidistant);
    }

    #loadCommits(response: CommitsResponse): Commit[] {
        const commits = new Map<string, Commit>();
        const commitsByHash = [];

        for (const [idx, hash] of response.hashByHash.entries()) {
            const commit = {
                indexByHash: idx,
                indexByGraph: NaN, // Filled in later
                hash,
                parents: [],
                children: [],
                author: response.authorByHash[idx]!,
                committerDate: response.committerDateByHash[idx]!,
                summary: response.summaryByHash[idx]!,
            };
            commits.set(hash, commit);
            commitsByHash.push(commit);
        }

        // Fill in parents and children
        for (const [childIdx, parentIdx] of response.childParentIndexPairs) {
            const childHash = response.hashByHash[childIdx]!;
            const parentHash = response.hashByHash[parentIdx]!;

            const child = commits.get(childHash)!;
            const parent = commits.get(parentHash)!;

            child.parents.push(parent);
            parent.children.push(child);
        }

        return commitsByHash;
    }

    #sortCommitsByCommitterDate(commits: Commit[]) {
        commits.sort((a, b) => a.committerDate - b.committerDate);
    }

    /**
     * Sort commits topologically such that parents come before their children.
     *
     * Assumes that there are no duplicated commits anywhere.
     *
     * A reverse post-order DFS is a topological sort, so that is what this
     * function implements.
     */
    #sortCommitsTopologically(commits: Commit[]): Commit[] {
        const visited: Set<string> = new Set();
        const visiting: Commit[] = commits.filter(c => c.parents.length == 0);

        const sorted: Commit[] = [];

        while (visiting.length > 0) {
            const commit = visiting.at(-1)!;
            if (visited.has(commit.hash)) {
                visiting.pop();
                sorted.push(commit);
                continue;
            }

            for (const child of commit.children) {
                if (!visited.has(child.hash)) {
                    visiting.push(child);
                }
            }

            visited.add(commit.hash);
        }

        sorted.reverse();

        console.assert(visited.size === commits.length);
        console.assert(visiting.length === 0);
        console.assert(sorted.length === commits.length);
        return sorted;
    }

    /**
     * Assumes the times are sorted.
     */
    #makeDayEquidistant(times: number[]): number[] {
        const days: { day: number, amount: number; }[] = [];
        for (const time of times) {
            const day = time % SECONDS_PER_DAY;
            const prev = days.at(-1);
            if (prev === undefined || prev.day !== day) {
                days.push({ day, amount: 1 });
            } else {
                prev.amount++;
            }
        }

        const result: number[] = [];
        for (const day of days) {
            const secondsPerCommit = SECONDS_PER_DAY / day.amount;
            for (let i = 0; i < day.amount; i++) {
                const time = day.day * SECONDS_PER_DAY + secondsPerCommit * (i + 0.5);
                result.push(time);
            }
        }

        return result;
    }

    #epochTimesToDates(times: number[]): Date[] {
        return times.map(t => new Date(1000 * t));
    }
}