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machine.js

const inProcessStates = {
  states: {
    PROCESSING_DATA: {
      // I still need to figure out how to do activities correctly, ordering isn't correct as I can't pass this activity
      // to it's children
      activities: [{
        type: 'activity',
        message: 'Reprocessing static & page queries'
      }],
      invoke: {
        src: 'runQueries',
        onDone: {
          target: 'DONE',
          actions: assign({
            queryIds: [],
          })
        }
      },
    },
    PROCESSING_WEBPACK: {
      entry: ['buildCode'],
      activities: [{
        type: 'activity',
        message: 'Rebuilding production JavaScript and CSS bundles'
      }],
      on: {
        SUCCESS: {
          target: 'DONE',
          actions: assign({
            prevWebpackHashMap: (_, event) => event.chunkHashes,
            pagesToBuild: (_, event) => event.pages,
          })
        }
      }
    },
    DONE: {
      on: {
        '': [
          {
            target: '#write-pages',
            cond: (ctx) => ctx.pagesToBuild && ctx.pagesToBuild.length,
          },
          {
            target: '#build-complete',
          }
        ]
      }
    }
  },
}

const incBuildMachine = Machine({
  id: 'inc-build',
  initial: 'PENDING',

  context: {
    program: null,
    pagesToBuild: [],
    queryIds: [],
    prevWebpackHashMap: new Map(),
    reporter: null,
  },

  states: {
    PENDING: {
      invoke: {
        src: 'setup',
        onDone: {
          target: 'READY',
        }
      }
    },
    READY: {
      initial: 'PENDING',
      entry: ['notifyListeners'],
      states: {
        PENDING: {
          exit: ['notifyReady'],
          on: {
            BOOTSTRAP_FINISHED: {
              target: 'IDLE',
              actions: assign({ prevWebpackHashMap: (_, event) => event.chunkHashes }),
            },
          }
        },
        IDLE: {
          on: {
            DATA_CHANGE: {
              target: 'PROCESS.PROCESSING_DATA',
              actions: assign({
                queryIds: (ctx, event) => Array.from(new Set((ctx.queryIds || []).concat(event.queryIds)))
              })
            },
            CODE_CHANGE: {
              target: 'PROCESS.PROCESSING_WEBPACK',
            },
          }
        },
        PROCESS: inProcessStates,
        WRITE_PAGES: {
          id: 'write-pages',
          invoke: {
            src: 'writePages',
            onDone: {
              target: 'BUILD_COMPLETE',
            }
          },
        },
        BUILD_COMPLETE: {
          id: 'build-complete',
          invoke: {
            src: 'buildDone',
            onDone: {
              target: 'IDLE',
            }
          },
        }
      },
    },
  },
});