/**
 * "Executor" for running agentic workflows in parallel.
 * 
 * Notes & Features:
 * • Uses a layered topological sort to allow parallel block execution for blocks with no remaining dependencies.
 * • Each block's inputs are resolved through a template mechanism (e.g., <blockId.property>).
 * • Stores block outputs in context.blockStates so subsequent blocks can reference them by ID or name.
 * • Maintains robust error handling (if a block fails, throws an error for the entire workflow).
 * • Returns per-block logs that can be displayed in the UI for better trace/debug.
 */

import { SerializedWorkflow, SerializedBlock } from '@/serializer/types'
import { BlockOutput } from '@/blocks/types'
import {
  Tool,
  ExecutionContext,
  ExecutionResult,
  BlockLog
} from './types'
import { tools } from '@/tools'

export class Executor {
  constructor(
    private workflow: SerializedWorkflow,
    // Initial block states can be passed in if you need to resume workflows or pre-populate data.
    private initialBlockStates: Record<string, BlockOutput> = {}
  ) {}

  /**
   * Main entry point that executes the entire workflow in parallel layers.
   */
  async execute(workflowId: string): Promise<ExecutionResult> {
    const startTime = new Date()

    // Build the ExecutionContext with new blockLogs array
    const context: ExecutionContext = {
      workflowId,
      blockStates: new Map<string, BlockOutput>(),
      blockLogs: [],
      metadata: {
        startTime: startTime.toISOString()
      },
    }

    // Pre-populate block states if initialBlockStates exist
    Object.entries(this.initialBlockStates).forEach(([blockId, output]) => {
      context.blockStates.set(blockId, output)
    })

    try {
      // Perform layered parallel execution
      const lastOutput = await this.executeInParallel(context)

      const endTime = new Date()
      context.metadata.endTime = endTime.toISOString()

      // Return full logs for the UI to consume
      return {
        success: true,
        output: lastOutput,
        metadata: {
          duration: endTime.getTime() - startTime.getTime(),
          startTime: context.metadata.startTime!,
          endTime: context.metadata.endTime!,
        },
        logs: context.blockLogs,
      }
    } catch (error) {
      return {
        success: false,
        output: { response: {} },
        error: error instanceof Error ? error.message : 'Unknown error',
        logs: context.blockLogs,
      }
    }
  }

  /**
   * Executes all blocks in a layered topological fashion, running each layer in parallel via Promise.all.
   * If a cycle is detected, throws an error.
   */
  private async executeInParallel(context: ExecutionContext): Promise<BlockOutput> {
    const { blocks, connections } = this.workflow

    // Build in-degree and adjacency list for each block
    const inDegree = new Map<string, number>()
    const adjacency = new Map<string, string[]>()

    // Initialize inDegree and adjacency
    for (const block of blocks) {
      inDegree.set(block.id, 0)
      adjacency.set(block.id, [])
    }

    // Populate edges
    for (const conn of connections) {
      inDegree.set(conn.target, (inDegree.get(conn.target) || 0) + 1)
      adjacency.get(conn.source)?.push(conn.target)
    }

    // Start with all blocks that have inDegree = 0
    let layer = blocks
      .filter((b) => (inDegree.get(b.id) || 0) === 0)
      .map((b) => b.id)

    // Track the final output from the "last" block or set of blocks
    let lastOutput: BlockOutput = { response: {} }

    while (layer.length > 0) {
      // Execute current layer in parallel
      const results = await Promise.all(
        layer.map(async (blockId) => {
          // Find the block object
          const block = blocks.find((b) => b.id === blockId)
          if (!block) {
            throw new Error(`Missing block ${blockId}`)
          }

          // Resolve template references in block config params
          const resolvedInputs = this.resolveInputs(block, context)

          // Execute the block, store the result
          const output = await this.executeBlock(block, resolvedInputs, context)
          context.blockStates.set(block.id, output)
          return output
        })
      )

      // Keep track of the "most recent" result as lastOutput
      if (results.length > 0) {
        lastOutput = results[results.length - 1]
      }

      // Build the next layer by reducing in-degree of neighbors
      const nextLayer: string[] = []
      for (const blockId of layer) {
        const neighbors = adjacency.get(blockId) || []
        for (const targetId of neighbors) {
          const deg = inDegree.get(targetId) ?? 0
          const newDeg = deg - 1
          inDegree.set(targetId, newDeg)
          if (newDeg === 0) {
            nextLayer.push(targetId)
          }
        }
      }

      layer = nextLayer
    }

    // Validate that all blocks were executed. If not, the workflow has a cycle.
    const executedCount = [...inDegree.values()].filter((x) => x === 0).length
    if (executedCount !== blocks.length) {
      throw new Error('Workflow contains cycles or invalid connections')
    }

    return lastOutput
  }

  /**
   * Executes a single block by:
   *  1) Determining which tool to call
   *  2) Validating parameters
   *  3) Making the request (for http blocks or LLM blocks, etc.)
   *  4) Transforming the response via the tool's transformResponse
   */
  private async executeBlock(
    block: SerializedBlock,
    inputs: Record<string, any>,
    context: ExecutionContext
  ): Promise<BlockOutput> {
    const toolId = block.config.tool
    if (!toolId) {
      throw new Error(`Block "${block.id}" does not specify a tool`)
    }

    const tool: Tool | undefined = tools[toolId]
    if (!tool) {
      throw new Error(`Tool not found: ${toolId}`)
    }

    // Merge block's static params with dynamic inputs
    const validatedParams = this.validateToolParams(tool, {
      ...block.config.params,
      ...inputs,
    })

    // Prepare a new blockLog entry
    const blockLog: Partial<BlockLog> = {
      blockId: block.id,
      blockTitle: block.metadata?.title || 'Unnamed Block',
      startedAt: new Date().toISOString(),
    }

    try {
      if (!tool.request) {
        throw new Error(`Tool "${toolId}" has no request config.`)
      }

      const { url: urlOrFn, method: defaultMethod, headers: headersFn, body: bodyFn } =
        tool.request

      // Build the URL
      const url = typeof urlOrFn === 'function' ? urlOrFn(validatedParams) : urlOrFn
      // Determine HTTP method
      const methodFromParams =
        typeof validatedParams.method === 'object'
          ? validatedParams.method.method
          : validatedParams.method
      const method = methodFromParams || defaultMethod || 'GET'

      // Safely compute headers
      const headers = headersFn?.(validatedParams) ?? {}

      // Build body if needed
      const bodyNeeded = method !== 'GET' && method !== 'HEAD' && !!bodyFn
      const body = bodyNeeded
        ? JSON.stringify(bodyFn!(validatedParams))
        : undefined

      // Perform fetch()
      const response = await fetch(url || '', { method, headers, body })
      if (!response.ok) {
        // In case there is a custom transformError
        const transformError = tool.transformError ?? (() => 'Unknown error')
        const errorBody = await response.json().catch(() => ({
          message: response.statusText,
        }))
        throw new Error(transformError(errorBody))
      }

      // Transform the response
      const transformResponse =
        tool.transformResponse ??
        (async (resp: Response) => ({
          success: true,
          output: await resp.json(),
        }))

      const result = await transformResponse(response)
      if (!result.success) {
        const transformError = tool.transformError ?? (() => 'Tool returned an error object')
        throw new Error(transformError(result))
      }

      // Success: update the blockLog with success & output
      blockLog.success = true
      blockLog.output = result.output

      return { response: result.output }
    } catch (e) {
      blockLog.success = false
      blockLog.error = e instanceof Error ? e.message : 'Unknown error'
      throw e
    } finally {
      // Compute the end time and duration
      const end = new Date()
      blockLog.endedAt = end.toISOString()

      if (blockLog.startedAt) {
        const started = new Date(blockLog.startedAt).getTime()
        blockLog.durationMs = end.getTime() - started
      } else {
        blockLog.durationMs = 0
      }

      // Push the log entry
      context.blockLogs.push(blockLog as BlockLog)
    }
  }

  /**
   * Validates required parameters for a Tool, or uses defaults if present.
   */
  private validateToolParams(tool: Tool, params: Record<string, any>): Record<string, any> {
    return Object.entries(tool.params).reduce((acc, [name, config]) => {
      if (name in params) {
        acc[name] = params[name]
      } else if ('default' in config) {
        acc[name] = config.default
      } else if (config.required) {
        throw new Error(`Missing required parameter '${name}'`)
      }
      return acc
    }, {} as Record<string, any>)
  }

  /**
   * Resolves any template references in a block's config params (e.g., "<someBlockId.response>"),
   * pulling from context.blockStates. This is how outputs from one block get wired as inputs to another.
   */
  private resolveInputs(
    block: SerializedBlock,
    context: ExecutionContext
  ): Record<string, any> {
    const inputs = { ...block.config.params }

    // Create quick-lookup for blocks by ID and by normalized name
    const blockById = new Map(this.workflow.blocks.map((b) => [b.id, b]))
    const blockByName = new Map(
      this.workflow.blocks.map((b) => [
        b.metadata?.title?.toLowerCase().replace(/\s+/g, '') || '',
        b
      ])
    )

    const resolvedInputs = Object.entries(inputs).reduce(
      (acc, [key, value]) => {
        if (typeof value === 'string') {
          const matches = value.match(/<([^>]+)>/g)
          if (matches) {
            let resolvedValue = value
            for (const match of matches) {
              // e.g. "<someBlockId.response>"
              const path = match.slice(1, -1) // remove < and >
              const [blockRef, ...pathParts] = path.split('.')

              // Try blockRef as ID, then as normalized name
              let sourceBlock = blockById.get(blockRef)
              if (!sourceBlock) {
                const normalized = blockRef.toLowerCase().replace(/\s+/g, '')
                sourceBlock = blockByName.get(normalized)
              }

              if (!sourceBlock) {
                console.warn(`Block reference "${blockRef}" not found by ID or name.`)
                continue
              }

              const sourceState = context.blockStates.get(sourceBlock.id)
              if (!sourceState) {
                console.warn(`No state found for block ID "${sourceBlock.id}".`)
                continue
              }

              // Drill into the path
              let replacementValue: any = sourceState
              for (const part of pathParts) {
                if (!replacementValue || typeof replacementValue !== 'object') {
                  console.warn(`Invalid path part "${part}" in "${path}".`)
                  replacementValue = undefined
                  break
                }
                replacementValue = replacementValue[part]
              }

              // If a valid leaf is found
              if (replacementValue !== undefined) {
                // Replace the placeholder in the string
                resolvedValue = resolvedValue.replace(
                  match,
                  typeof replacementValue === 'object'
                    ? JSON.stringify(replacementValue)
                    : String(replacementValue)
                )
              } else {
                console.warn(`No value found at path "${path}".`)
              }
            }

            // Attempt JSON parse if it looks like JSON
            try {
              if (resolvedValue.startsWith('{') || resolvedValue.startsWith('[')) {
                acc[key] = JSON.parse(resolvedValue)
              } else {
                acc[key] = resolvedValue
              }
            } catch {
              acc[key] = resolvedValue
            }
          } else {
            // No placeholders
            acc[key] = value
          }
        } else {
          // Not a string param
          acc[key] = value
        }
        return acc
      },
      {} as Record<string, any>
    )

    return resolvedInputs
  }
}